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A putative protein-sequestration site involving intermediate filaments for protein degradation by autophagy. Studies with microinjected purified glycolytic enzymes in 3T3-L1 cells.

ABSTRACT: Several glycolytic enzymes (lactate dehydrogenase, pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase) were radiolabelled by [125I]iodination, conjugation with 125I-labelled Bolton & Hunter reagent and reductive [3H]methylation, and their degradative rates after microinjection into 3T3-L1 cells compared with that of the extracellular protein bovine serum albumin. Although the albumin remains largely cytosolic in recipient cells, the glycolytic enzymes rapidly (less than 30 min) become insoluble, as measured by detergent and salt extractions. The microinjected glycolytic enzymes appear to form disulphide-linked aggregates, are found in a cell fraction rich in vimentin-containing intermediate filaments and histones (nuclear-intermediate-filament fraction), and are degraded slowly by a lysosomal mechanism, as judged by the effects of inhibitors (NH4Cl, leupeptin, 3-methyladenine). 125I-labelled bovine serum albumin appears to be degraded rapidly and non-lysosomally. Prolonged treatment (96 h) of cultured cells with leupeptin results in the accumulation of pulse-labelled ([35S]methionine for 24 h) endogenous cell proteins in the detergent-and salt-non-extractable residue, but NH4Cl and 3-methyladenine do not have this effect. The findings are in terms of the interpretation of experiments involving microinjection of proteins to study intracellular protein protein degradation by autophagy.

SUBMITTER: Doherty FJ

PROVIDER: S-EPMC1147632 | biostudies-other | 1987 Feb

REPOSITORIES: biostudies-other

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Project description:Purpose: Mitochondrial dysfunction in adipose tissue has emerged as key to the development of obesity and diabetes. Salvianolic acid B (SalB) is a water-soluble ingredient derived from Salvia miltiorrhiza that has been shown to possess potential anti-obese and anti-diabetic activities. However, the cellular mechanism of SalB on mitochondrial function with respect to these metabolic disorders has not been elucidated. Therefore, we aim to investigate the effects of SalB on mitochondrial function in 3T3-L1 adipocytes and analyze the underlying molecular mechanism. Methods: The effects of SalB on adipocyte differentiation, glucose uptake, and glycerol release were evaluated in 3T3-L1 adipocytes. Differentiated adipocytes were treated with SalB (50 ?M) with or without PPAR? antagonist (GW9662, 20 ?M) for 48 h, and mitochondrial oxygen consumption rate (OCR) as well as extracellular acidification rate (ECAR) were assessed using an XF Extracellular Flux Analyzer. The mitochondrial distribution of adipocytes was assessed using Mito Tracker Green (MTG) and observed under a fluorescent microscope. In addition, the mRNA expression levels of peroxisome proliferators-activated receptor ?/? (PPAR?/?), CCAAT/enhancer binding protein? (C/EBP?), Nuclear respiratory factor 1/2 (NRF1/2), Uncoupling protein 2 (UCP2), and phosphofructokinase 2/fructose-2, 6-bisphosphatase 2 (PFKFB2) were detected by RT-PCR. Finally, changes in the protein levels of peroxisome proliferators-activated receptor ? coactivator-1? (PGC-1?) were determined by western blotting and immunofluorescence analysis. Results: Treatment with SalB increased glucose uptake and mitochondrial respiration, reduced glycerol release and promoted adipocyte differentiation by increasing mRNA expression of adipogenic transcription factors including PPAR?, C/EBP?, and PPAR?. Furthermore, SalB enhanced adipocytes mitochondrial content, mitochondrial respiration and glycolysis capacity, which had been attenuated by GW9662 treatment through the increased expression of PGC-1?. Conclusion: Our results provide novel insights into the role of PGC-1? and mitochondria as probable mediators of SalB activity in the regulation of adipocyte differentiation in 3T3-L1 adipocytes.

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A putative protein-sequestration site involving intermediate filaments for protein degradation by autophagy. Studies with microinjected purified glycolytic enzymes in 3T3-L1 cells.

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